1. Field of the Invention
The present invention relates to semiconductor devices. In particular, the invention relates to a method of electrical insulation in the case where the insulation distance between a casing and a power module housed in the casing is insufficient.
2. Description of the Background Art
Japanese Patent Laying-Open No. 2004-247684 discloses a structure of a semiconductor device having an inverter casing in which an intelligent power module (hereinafter also referred to as “IPM”) is housed. For this semiconductor device, a bus bar is provided on the upper side of the IPM. Further, the inverter casing is formed of a material having good thermal conductivity.
Although Japanese Patent Laying-Open No. 2004-247684 discloses no specific materials for the inverter casing, it is generally known that such materials as aluminum and iron are used for the inverter casing.
In recent years, with the energy-saving and environmental issues as a background, the hybrid vehicle having, as its motive-power sources, a DC supply, an inverter and a motor in addition to an engine has been of great interest and has already been in actual use.
The hybrid vehicle has a larger number of components mounted thereon such as the motor, inverter and high-voltage battery, as compared with the conventional motor vehicle having only an engine as a motive-power source. Therefore, for the hybrid vehicle, it is required to a great degree to downsize the mounted components and save space.
The inverter device is also required to decrease in size. Therefore, each of internal components themselves is decreased in size. Further, space is saved to the fullest extent. The realization of the space saving, however, could result in the case where a sufficient insulation distance between the electrically non-insulating portion of the IPM and the inverter casing cannot be ensured.
For example, regarding the semiconductor device disclosed in the above-referenced Japanese Patent Laying-Open No. 2004-247684 that has the high-voltage bus bar provided on the upper side of the IPM, space saving could result in an insufficient insulation distance between the bus bar and the inverter casing.
Then, the electrically non-insulating portion of the IPM may have electrical insulation capability or the inverter casing itself may have electrical insulation capability. These approaches, however, are generally accompanied by high costs and thus disadvantageous for the hybrid vehicle for which cost reductions are absolutely necessary.
Alternatively, an electrically insulating member may separately be provided to be attached to the inverter casing or IPM. These approaches, however, require an additional space for attaching the electrically insulating member to the inverter casing or IPM, thereby hindering realization of the space saving.